WR-90 waveguide has wall spacing

PHYSICS · Multi-part · Fermi University Physics · Electricity, Magnetism & Electromagnetism · Electromagnetic waves and their propagation · Electromagnetic waves and their propagation

Modes, Packets and Media, Ch Transmission lines and electromagnetic waves in matter, plasmas and guides

Problem

a = 22.86\,\mathrm{mm}

, giving its lowest mode a cutoff frequency of

6.56\,\mathrm{GHz}

. It is driven at

4.00\,\mathrm{GHz}

, below cutoff, so the field decays as

e^{-\alpha z}

. Take

c = 2.998\times10^{8}\,\mathrm{m\,s^{-1}}

. ((a)) Find the attenuation

\alpha

in decibels per centimetre (of power). ((b)) Find the fraction of the input field amplitude remaining after

5.0\,\mathrm{cm}

of guide.

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